1. The Field of the Invention
The present invention relates to a ceramic member which exhibits high corrosion resistance to halogenous-corrosive gases or plasma thereof. More particularly, the present invention relates to such a corrosion-resistant ceramic member used in a system utilizing halogen plasma for producing semiconductor devices.
2. Prior Art
Recently, there have been developed systems utilizing halogen plasma, for example, for plasma processing including plasma dry etching or plasma coating adopted in production processes of semiconductor devices, and for discharge lamps, metal halide lamps and the like. With respect to a plasma process for producing semiconductor devices, a large variety of high-reactive halogenous-corrosive gases, containing fluorine, chlorine, etc. have been used for the etching and cleaning of semiconductor substrates. Since these gases and plasma thereof corrode members in the processing systems, the members used in these purposes require high corrosion resistance to halogenous plasma.
FIG. 1 shows an example of a processing chamber used for halogen-plasma etching or cleaning systems for producing semiconductor devices. This chamber includes a chamber wall 1, with a high frequency induction coil 6 arranged on the outside of the chamber to generate plasma. A shower head 2 is fixed at the upper portion inside the chamber wall 1 to supply a gas mixture containing a halogen gas into the chamber, and a lower electrode 4, or a stage, is arranged at the lower portion in order to fix and mount a wafer 5 to be processed thereon. Furthermore, a clamp ring 3 for fixing the wafer 5 is mounted on the lower electrode.
Except for work pieces such as the semiconductor wafer to be processed, the members such as chamber wall 1, shower head 2 and clamp ring 3 have been made of corrosion-resistant material such as quartz, stainless steel, alumina or the like. Also, there have been utilized sintered materials of alumina or aluminum nitride, and materials obtained by coating these ceramic sintered materials with a ceramic film of silicon carbide (see JP(B)-5-53872, JP(A)3-217016 and JP(A)8-91932).
However, quartz glass conventionally used is drastically consumed in halogen plasma because of poor corrosion resistance thereto. Particularly, quartz glass is etched by fluorine or chlorine plasma on the surface. Quartz glass, which is often required to be high in transparency, is easily hazed into white on the surface by the plasma, then, losing its transparency.
A member made of a metal such as stainless steel has also low corrosion resistance to halogen plasma, then causing the problem that the wafer while being processed is contaminated by generation of metal halide particles attended with the corrosion.
Sintered materials of aluminum oxide or aluminum nitride, or ceramic materials obtained by coating this sintered material with a ceramic film of silicon carbide is higher in corrosion resistance to halogenous plasma as compared with quartz glass or corrosion-resistant metals. However, when they are exposed to plasma, halides are evaporated and consumed from surfaces of the aluminum-based sintered material or from between grain boundaries in the material, resulting in gradually developing corrosion of the ceramic material. This is because aluminum halide formed from the material reacting with halogenous plasma has a low melting temperature.
In dry etching or cleaning processes, also, ceramic material members have another problem of generating, by corrosion, particles which cause open or short circuit of metal wiring parts or interconnections on a semiconductor device, thereby deteriorating the device characteristics.
These particles result from corroding the members, such as an inner wall, a clamp ring, etc., which constitute the inner portions of the halogenous plasma treating chamber, by halogenous-corrosive gases and their plasma. The particle compound is evaporated by corrosion reaction of an component in the material with halogen plasma, and is repeatedly accumulated onto the inner wall of the chamber made of a high corrosion-resistant material.
Therefore, for the purpose of preventing the evaporated halide from accumulating as a deposit onto the chamber inner wall, the halide is evaporated and discharged by heating the chamber outer wall using infrared lamps. Therefore, not only high heat resistance, but also high thermal conductivity is required to members used in the chamber.
The present inventors have found that rare-earth-containing compounds form halides with a high melting point and high corrosion resistance even if the halide is produced as a result of reaction with the halogenous-corrosive gas or plasma thereof, then, proposing the rare-earth-containing compounds as members for plasma processing systems which are used for production of semiconductors (see Japanese Patent Publications (A)10-45467 and (A)10-236871).
However, since the rare-earth-containing compounds such as yttria Y2O3 and yttrium-aluminum-garnet (YAG), which are considered to be suited for practical use, have low thermal conductivity of 10 W/mK or less, heat quantity added is not distributed uniformly all over the wall even when heating outside the chamber wall for the purpose of preventing the halide deposition from accumulating onto the chamber inner wall, thus obtaining only a local effect of preventing halide deposition.
A proposal has been made to improve the corrosion resistance and heating uniformity by forming a thin film made of a rare-earth-containing compound on the surface of a substrate having high thermal conductivity such as conventional AlN substrate; however, there arose a problem that the thin film is peeled off on heating the substrate due to a difference in thermal expansivity between the substrate and thin film.
Also, the outer wall of the chamber is often heated rapidly to high temperatures using lamps for preventing halide accumulation onto the chamber inner wall, and therefore thermal-shock resistance, together with the corrosion resistance and thermal conductivity, is required to ceramic members used as such parts inside the chamber.
An object of the present invention is to provide a ceramic member having high corrosion resistance to halogenous gas and plasma thereof.
Another object of the present invention is to provide a ceramic member having thermal conductivity enough to prevent accumulation of a deposit over the whole member by external heating.
Still another object of the present invention is to improve the thermal-shock resistance of the ceramic member in the use under high temperature in halogen plasma.
A ceramic member in the present invention is provided to contain not less than 10% by volume of a phase of an oxide compound of a rare earth metal and aluminum, in other words, a double oxide of rare earth metal oxide and aluminum oxide, and at least one oxide phase selected from aluminum oxide, yttrium oxide and aluminum nitride as the main balance.
In the ceramic member of the invention, the oxide compound of rare earth metal and aluminum is preferably yttrium-aluminum-garnet (hereinafter referred to as YAG). The oxide compound may have another structure of millet or perobskite composed of yttrium and aluminum.
A ceramic member of the present invention contains a phase of YAG of not less than 10% by volume and a phase of yttrium oxide as the main balance, wherein the amount of yttrium in ceramic member is within a range of 35 to 80 mole % in terms of yttrium oxide and the amount of aluminum is within a range of 20 to 65 mole % in terms of aluminum oxide in the ceramic member, thereby, improving corrosion resistance of the ceramic member with respect to halogen plasma, and also increasing sintering performance significantly to obtain dense sintered material.
The ceramic member of the present invention may includes, as a main crystalline phase, a single YAG single phase, or a mixed phase of the YAG phase and an alumina phase, or a mixed phase of the YAG phase and an yttria phase, and contains zirconium oxide or cerium oxide. The addition of zirconia or ceria into the ceramic material containing the YAG phase improves the thermal-shock resistance without impairing the corrosion resistance. In the present invention, a thermal-shock resistance requires not less than 100xc2x0 C. as thermal-shock resistance temperature xcex94T defined hereinafter.
Zirconium oxide is present as a phase between the grain boundaries of the main crystalline, which phase preferably contains cerium oxide as a stabilizer, whereby zirconia to be added is stabilized to form a tetragonal crystalline structure by cerium.
In the present invention, cerium oxide may be independently added to a single phase of YAG to improve the relative density of the YAG sintered material to 99% or more, and the resulting YAG sintered material can exhibits high corrosion resistance even when exposed to halogen plasma.
In a ceramic member of the present invention, the volume of a compound of rare earth metal oxide and aluminum oxide is preferably within a range of 10 to 60% and the balance may be aluminum oxide or aluminum nitride. This ceramic member employs a structure of the ceramic body where the compound phase of rare earth metal oxide and aluminum oxide, especially, YAG phase, is dispersed in the form of grains in a matrix of aluminum oxide or aluminum nitride within the above range, thereby, realizing a ceramic member which exhibits high corrosion resistance to halogen plasma and has high thermal conductivity of not less than 20 W/mK due to aluminum oxide or aluminum nitride matrix, so as effectively to prevent accumulating the particle deposit by heating.